1. Field of the Invention
The invention relates to an apparatus for managing a local area network, in particular, it relates to a switching mechanism that is used to manage the physical layer of a local area network.
2. Background Art
Local area networks (LANs) provide a popular, cost effective way of interconnecting many computing resources (e.g. personal computers, minicomputers or workstations) within an enterprise. The backbone of the LAN is a wiring system that provides a physical transmission medium for interconnecting the computing resources. The wiring system may be coaxial cable, shielded or unshielded copper wire, or fiber optic cable. For each computing resource there is a transceiver that provides the electrical connection or interface between the computing resource and the wiring system. The transceiver converts the information from the computing resource into the actual signals that propagate over the wiring system. The LAN also includes network software which assembles the messages into the format required by the particular protocol used for communication over the network.
A common LAN configuration is the ring network. It is so named because the computing resources or stations are connected together through a series of point-to-point cables to form a ring. Such ring networks are thus inherently ordered, each station having an upstream neighbor from which it receives information and a downstream neighbor to which it transfers information. In one of the oldest and most commonly used ring networks, a bit pattern, referred to as a token, circulates around the ring from one station to the next. When a station has something to send to another station, it captures the token and gains the right to transmit information over the network. When its transmission is complete, it releases the token so that some other station can gain the right to transmit over the network.
Typically, the actual physical interconnections in the ring network occur at one or more central locations referred to as wiring closets. For each station in the ring, cables are run into the wiring closet that carry communications to and from that station. In such systems, when reconfiguring the ring becomes necessary for any reason (e.g. for maintenance and repair or changing needs of the network users), it is necessary to go into the wiring closets and manually rewire the interconnections. This, of course, can be a time consuming and difficult job. In addition, physically disturbing the cables and the interconnections increases the risk that network failures will occur.
In general, the invention features a wiring hub for interconnecting a plurality of network components to form a local area network. The wiring hub includes a data signal bus and a programmable switching mechanism connected to the data signal bus. The switching mechanism includes a plurality of ports each of which can be electrically coupled to a different one of the plurality of network components to pass communications signals to, and receive communications signals from, the network component to which it is coupled. The programmable switching mechanism interconnects a selectable set of the plurality of ports together through the data signal bus and in any user selectable ordered sequence.
In one implementation, the wiring hub includes a passive backplane that contains the data signal bus and a plurality of connectors connecting to the data signal bus. The switching mechanism includes a plurality of port module cards each of which is plugged into a different one of the plurality of connectors on the backplane. Each of the port module cards includes a different subset of the plurality of ports. The bus includes a plurality of signal lines and each of the port module cards includes a plurality of multiplexers equal in number to the number of ports on that card. Each of the multiplexers on a port module card is associated with a different one of the ports on that card and is able to electrically couple a signal from any one of the plurality of signal lines of the bus to the port with which that multiplexer is associated. The port module cards each include a plurality of driver modules equal in number to the number of ports on that card and each of which is associated with a different one of the ports on that card. Each driver module is assigned to drive a different one of the plurality of signal lines on the bus. Each driver module includes a left driver and a right driver. The left driver drives one side of its assigned signal line and the right driver drives the other side of its assigned signal line.
The wiring hub may also include a controller card that generates control signals to control the operation of the programmable switching mechanism. The backplane includes a control bus to which the control card and the port module cards are electrically coupled. The control bus carries the control signals to the port module cards to control the multiplexers on them. The wiring hub includes two power supply cards connected to the power bus and the backplane includes a power bus to which the power supplies are connected. Power is supplied over the power bus to the control card and the plurality of port module cards, which are also electrically connected to the power bus.
The data signal bus includes a plurality of signal lines, and the programmable switching mechanism includes a full, non-blocking matrix switch having a plurality of input terminals equal in number to the plurality of signal lines and a plurality of output terminals equal in number to the plurality of ports. Each of the input terminals receives a signal from a different one of the plurality of signal lines and each of the output terminals provides a signal to a different one of the plurality of ports. The matrix switch is able to electrically couple the signal from any one of the input terminals to any one of the output terminals. The programmable switching mechanism also includes a set of configuration registers. The matrix switch is configured by writing configuration information to that set of registers. The configuration information identifies which input terminals are to be electrically coupled to which output terminals. The controller module controls the matrix switch by writing control information to the set of configuration registers. The wiring hub further includes means for determining the state of each of the plurality of ports and means for recording the state of the plurality of ports. The controller module includes means for reading the state recording means and means for reconfiguring the matrix switch in response to detecting a change in state.
One advantage of the invention is that it enables the network manager to easily control and modify the configuration of a local area network from a central location without having to physically rearrange wiring and cables in wiring closets. The rearrangement of connections is done automatically by a switching mechanism under software control. Also, the invention enables the network manager to connect the stations in any order and in any of a number of different local area networks. Furthermore, use of a passive backplane yields additional significant advantages in terms of system reliability and ease of maintenance. Since active components are more often the cause of system failures, keeping active components off of the backplane greatly reduces the likelihood of having to repair the backplane. If all of the active components are only on the cards which plug into the backplane (i.e., the port cards, the RI/RO cards, the controller and the power supplies), then a failure of one of the active components can be fixed by merely replacing the card. In general, repairs to backplanes typically remove the system from service for a significant period of time. The use of the passive backplane greatly reduces the likelihood that repairs will ever have to be done to the backplane.
Other advantages and features will become apparent from the following description of the preferred embodiment read in connection with the accompanying drawings.